Why does getting up in the morning get harder in autumn?
― Your body clock is set by morning light, not by an alarm
In summer you were waking up before your alarm even rang. Then, around late September, suddenly you can't drag yourself out of bed. Same bedtime, same room. It isn't willpower, and it isn't age. This time of year, the "morning light" that reset your body every day is slowly starting to arrive late.
Back in summer, white light would slip through the curtain gap before the alarm even rang, and your eyes would open on their own. You'd check the clock — not even 6am yet.
But once the autumn equinox passes, the same 6:30 alarm goes off and the room is still dim. Your head stays foggy, and your body just won't leave the bed.
You haven't been staying up late. So why has so much changed in just a few weeks?
There are two main reasons
Left alone, the clock built into your body is thought to drift about 10 minutes late each day. What resets it back to "morning" every day is strong light hitting your eyes.
Sunrise gets a little later every day from autumn into winter. You're still waking at the same time, but the signal keeps sliding back. The one who resets your clock keeps showing up late.
Put these two together, and even though you wake at the same time, your body is still running on its "night setting." Let's look at each in turn.
The clock inside you gets reset every morning
Just behind your eyes sits a cluster of nerve cells far smaller than a grain of rice. This is the master clock that sets the timing for your whole body. When to raise your temperature, when to release the substance that makes you sleepy — it directs the whole day's schedule.
This master clock isn't accurate unless it stays connected to the outside world. In experiments where people live in rooms with no light at all, a person's day is known to run a little longer than 24 hours. Left unchecked, that means drifting a little later, day after day, toward a night-owl schedule.
Morning light is what cancels out that drift. When strong light hits your eyes, the signal travels straight to the master clock, and the hands get reset to "it's morning." At the same time, the release of the sleep-inducing substance stops, and your temperature and blood pressure start to climb. The alarm sound wakes your mind, but it's light that wakes your body.
In autumn, that light arrives a little later every day
This is where the season matters. In Tokyo, sunrise is roughly 4:25am around the summer solstice, about 5:30am in late September, and roughly 6:47am around the winter solstice. From late September into winter, sunrise slides back by more than an hour.
Look at Figure 1. Say you wake at 6:30. In summer, it was already light more than two hours before you got up — plenty of light even through the curtains. By late September, there's only about an hour between daybreak and wake-up time. In winter, sunrise hasn't even happened yet when you get up.
The body clock can't shift much in a single day. If the signal arrives tens of minutes late, your body's wake-up preparations run just as late. The struggle isn't weak willpower — your body is still running on its "night setting." That foggy feeling right after waking is this time lag itself.
In brightness units, indoor lighting runs to roughly a few hundred, while outdoors on a cloudy day it's typically several thousand up to over 10,000. Your body clock responds to this order-of-magnitude difference. Turning on a room light isn't enough of a signal, but stepping outside — even under clouds — is plenty. As in Why do you still get sunburned on a cloudy day?, clouds cut light by far less than you'd think.
As days get shorter, the sleep-inducing substance also starts releasing earlier in the evening. That's why autumn can bring the seemingly contradictory feeling of "getting sleepy earlier at night, yet unable to get up in the morning." Both come from the same underlying cause — the changing length of daylight.
Summary
Autumn mornings feel hard because the morning light that used to keep your body clock in sync keeps sliding later along with sunrise. Your wake-up time stays fixed, so your body's schedule and society's schedule gradually drift apart. The fix lies in the same place: open the curtains the moment you wake, and get even a few minutes of outdoor light if you can. Hand the signal over early, and your body will start moving to match it.
Struggling to get up isn't a matter of willpower.
It's just that the signal driving your body clock is running late.
What your body does while you're asleep is covered in Why do we need to sleep?, and how day length affects another part of the body is in Why does hair shedding increase in autumn?.
- For one week, note your wake-up time and how you felt on waking, on a 3-point scale (fresh / okay / rough). Also jot down that day's sunrise time (check a newspaper or calendar page).
- For the next week, throw the curtains fully open the moment you wake, and if you can, step outside for just 5 minutes — then keep the same log. Keep your bedtime the same throughout.
- Line up both weeks and compare. Check whether how you feel on waking changes, and how much later sunrise got over that week.
*How you feel is also affected by weather and health, so don't judge from a single day — look at the week's average instead. If poor sleep continues, please consult a doctor rather than self-diagnosing.
Want to go deeper? ― Terms, formulas, and how this maps onto the curriculumWe flag which level each part belongs to, from middle school through university
- MSCovered in middle-school science
- HSCovered in high-school "Biology Basics / Biology"
- HS+Advanced high-school content, or textbook sidebar material
- Univ.Not taught in high school — university-level content (chronobiology, physiology)
- ResearchNot yet settled even at university level — an active research question
MSTerms: this phenomenon has a name
- Circadian rhythm: fluctuations in temperature, hormones, sleepiness and more that repeat on a roughly 24-hour cycle. It continues even without light and dark cues.
- Suprachiasmatic nucleus: a small cluster of nerve cells at the base of the brain, just above where the optic nerves cross. This is the body's master clock.
- Melatonin: a hormone released in larger amounts at night that signals "it's nighttime" to the body. Strong light stops its release.
- Entrainment: the daily resetting of the body clock to match the outside light-dark rhythm. The cue that does the resetting is called a zeitgeber.
MSHSDo the math: how much later does sunrise get in a week?
Let's put a number on how fast autumn mornings get harder, as a sunrise delay. Converting times to minutes makes this easier. We'll count minutes elapsed since midnight.
| Late-September sunrise (rough value for Tokyo) | 5:30am (330 min from midnight) |
| Late-December sunrise (rough value for Tokyo) | 6:47am (407 min from midnight) |
| Days between them | about 90 days |
| Total delay in sunrise (min) | 407 − 330 ＝ 77 |
| Delay per day (min) | 77 ÷ 90 ≒ 0.86 |
| Delay per week (min) | 0.86 × 7 ≒ 6 |
The morning signal slides back by roughly 6 minutes a week, and about 25 minutes over a month. Each day's change is too small to notice, but add it up over a month and it becomes large enough to feel.
HSHS+Which way light shifts the clock depends on when you're exposed
HSBesides the cells that sense light and dark, the retina contains cells that respond strongly to blue wavelengths and connect directly to the brain's master clock. This pathway is separate from the one used for seeing. Even in some people with impaired vision, if this pathway remains intact, the rhythm can still be maintained.
HS+The same intensity of light shifts the clock forward if seen in the morning, and backward if seen at night. A chart mapping this effect by time of day is called a phase response curve. Staring at a bright screen at night pushes sleep later because it's acting on the night side of this curve.
Univ.Every single cell has its own clock
Inside the master clock, several genes form a loop that suppresses each other's activity, and the cycle of proteins building up and breaking down takes roughly 24 hours. The same mechanism exists in cells throughout the body — the liver, the skin, and more — and the master clock acts as the conductor keeping them all in sync. Meal timing is known to shift the liver's clock and others even before it shifts the brain's.
ResearchWhat's still not fully understood
- Where individual differences in cycle length come from Genetic differences are thought to play a role in whether someone is a "morning type" or "night type," but how much is innate versus shaped by habit hasn't been clearly separated out.
- Seasonal low mood It's known that some people's mood dips during shorter-daylight periods, but debate continues over which factor — amount of light, timing, or circadian misalignment — is mainly responsible.
- Long-term effects of artificial lighting How decades of evening light exposure affect health is hard to determine through long-term tracking, and no conclusion has been reached.
In other words, this article too reflects only "what's understood so far." In particular, the exact prescription — how many minutes of light, at what time — varies from person to person.
How this maps onto the curriculum (by level)
| Level | Subject / unit | Where in this article |
|---|---|---|
| MS | Science, earth science strand (sun's motion and seasons) / Health & PE (lifestyle habits) | How sunrise time changes with season, Figure 1 |
| HS | Biology Basics (maintaining the internal environment / hormones) | The explanation of melatonin and the temperature rhythm |
| HS+ | Biology (sensory reception, advanced topics) | How the clock's shift direction depends on light-exposure timing |
| Univ. | Chronobiology, physiology, molecular biology | The clock-gene loop and clocks throughout the body's cells |
| Research | Sleep medicine, light-environment research | Individual variation and long-term effects of evening lighting |
| ― | Everyday connection | Open the curtains on waking, get morning outdoor light |
- National Astronomical Observatory of Japan, Koyomi Calculation Room (国立天文台 暦計算室) (sunrise/sunset time calculations)
- Ministry of Health, Labour and Welfare (厚生労働省), "Sleep Guide for Health 2023" (健康づくりのための睡眠ガイド2023)
- Ministry of Health, Labour and Welfare (厚生労働省), Lifestyle Disease Prevention Health Information Site, "How the Body Clock and Sleep Work" (体内時計と睡眠のしくみ)
- Czeisler CA, et al., "Stability, precision, and near-24-hour period of the human circadian pacemaker," Science, 1999 (a study measuring the human circadian clock's period under controlled light conditions)
*This article is a general-audience science explainer. The figures given are approximations meant to illustrate the mechanism. Sunrise time varies by location and year. If you experience persistent strong sleepiness or insomnia, please consult a medical professional rather than self-diagnosing from this article.